AVG function in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate the average salary from the employees table.

MySQL

SELECT [1](salary) FROM employees;

Drag options to blanks, or click blank then click option'

AAVG

BMAX

CCOUNT

DSUM

Attempts:

3 left

💡 Hint

Common Mistakes

Using SUM instead of AVG will give the total, not the average.

Using COUNT will count rows, not calculate average.

The AVG function calculates the average value of a numeric column.

2fill in blank

medium

Complete the code to find the average price from the products table where category is 'Books'.

MySQL

SELECT AVG(price) FROM products WHERE category = [1];

Drag options to blanks, or click blank then click option'

A"Books"

BBooks

C'Books'

DBooks'

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around string values causes syntax errors.

Using double quotes may not work depending on SQL mode.

String values in SQL must be enclosed in single quotes.

3fill in blank

hard

Fix the error in the code to correctly calculate the average age from the users table.

MySQL

SELECT AVG[1]age FROM users;

Drag options to blanks, or click blank then click option'

A{age}

Bage

C[age]

D(age)

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting parentheses causes syntax errors.

Using brackets or braces is invalid in SQL function calls.

The AVG function requires parentheses around the column name.

4fill in blank

hard

Fill both blanks to calculate the average score for students with grade greater than 80.

MySQL

SELECT [1](score) FROM students WHERE grade [2] 80;

Drag options to blanks, or click blank then click option'

AAVG

B>

C<

DSUM

Attempts:

3 left

💡 Hint

Common Mistakes

Using SUM instead of AVG will sum scores, not average.

Using < instead of > will select wrong rows.

Use AVG to calculate average and > to filter grades greater than 80.

5fill in blank

hard

Fill all three blanks to calculate the average price for products with stock less than 50 and category 'Electronics'.

MySQL

SELECT [1](price) FROM products WHERE stock [2] 50 AND category = [3];

Drag options to blanks, or click blank then click option'

AAVG

B<

C'Electronics'

DSUM

Attempts:

3 left

💡 Hint

Common Mistakes

Using SUM instead of AVG.

Forgetting quotes around 'Electronics'.

Using > instead of < for stock condition.

Use AVG for average, < for less than, and single quotes around string 'Electronics'.

Practice

1. What does the AVG() function do in MySQL?

easy

A. Returns the sum of all values in a column

B. Counts the number of rows in a table

C. Finds the maximum value in a column

D. Calculates the average value of a numeric column

Solution

1. Step 1: Understand the purpose of AVG()

   The AVG() function is designed to calculate the average (mean) of numeric values in a column.

2. Step 2: Compare with other aggregate functions

   Unlike COUNT(), MAX(), or SUM(), AVG() specifically returns the average value.

3. Final Answer:

   Calculates the average value of a numeric column -> Option D

4. Quick Check:

   AVG() = average [OK]

Hint: AVG() always returns the mean of numeric values [OK]

Common Mistakes:

• Confusing AVG() with COUNT()
• Thinking AVG() sums values instead of averaging
• Assuming AVG() includes NULL values in calculation

2. Which of the following is the correct syntax to find the average salary from a table named employees?

easy

A. SELECT AVG(salary) FROM employees;

B. SELECT AVG salary FROM employees;

C. SELECT AVERAGE(salary) FROM employees;

D. SELECT salary AVG() FROM employees;

Solution

1. Step 1: Recall correct AVG() syntax

   The correct syntax uses AVG() as a function with the column name inside parentheses.

2. Step 2: Check each option

   SELECT AVG(salary) FROM employees; uses AVG(salary) correctly. Options A, C, and D have syntax errors or wrong function names.

3. Final Answer:

   SELECT AVG(salary) FROM employees; -> Option A

4. Quick Check:

   AVG(column) syntax [OK]

Hint: AVG() requires parentheses around the column name [OK]

Common Mistakes:

• Omitting parentheses in AVG()
• Using wrong function name like AVERAGE()
• Placing AVG() after column name incorrectly

3. Given the table scores with values:
id | score
1 | 80
2 | 90
3 | NULL
4 | 70
What will the query SELECT AVG(score) FROM scores; return?

medium

A. 80

B. NULL

C. 80.0

D. 75

Solution

1. Step 1: Identify values considered by AVG()

   AVG() ignores NULL values, so it averages 80, 90, and 70.

2. Step 2: Calculate average of non-NULL scores

   (80 + 90 + 70) / 3 = 240 / 3 = 80.0. MySQL's AVG() returns a floating-point value.

3. Final Answer:

   80.0 -> Option C

4. Quick Check:

   AVG ignores NULL, average = 80.0 [OK]

Hint: AVG ignores NULLs and returns float average [OK]

Common Mistakes:

• Including NULL in average calculation
• Expecting integer instead of float result
• Confusing AVG with SUM or COUNT

4. Consider this query:
SELECT AVG(price) FROM products WHERE price > 0;
It returns NULL even though there are products with positive prices. What is the likely cause?

medium

A. The price column contains only NULL values

B. The WHERE clause filters out all rows

C. AVG() cannot be used with WHERE clause

D. The table products does not exist

Solution

1. Step 1: Understand AVG() behavior with WHERE clause

   The WHERE clause filters rows before AVG() calculates the average.

2. Step 2: Analyze why AVG() returns NULL

   If the WHERE clause excludes all rows (no price > 0), AVG() has no values to average and returns NULL.

3. Final Answer:

   The WHERE clause filters out all rows -> Option B

4. Quick Check:

   Empty filtered rows cause AVG() to return NULL [OK]

Hint: Check WHERE filters; no rows means AVG() returns NULL [OK]

Common Mistakes:

• Assuming AVG() ignores WHERE clause
• Thinking AVG() returns 0 if no rows
• Believing AVG() cannot be combined with WHERE

5. You have a sales table with columns region and amount. How do you write a query to find the average sales amount per region, excluding regions with no sales?

hard

A. SELECT region, AVG(amount) FROM sales GROUP BY region HAVING AVG(amount) > 0;

B. SELECT region, AVG(amount) FROM sales WHERE amount IS NOT NULL GROUP BY region;

C. SELECT region, AVG(amount) FROM sales GROUP BY region WHERE amount > 0;

D. SELECT region, AVG(amount) FROM sales GROUP BY region HAVING amount > 0;

Solution

1. Step 1: Group sales by region

   Use GROUP BY region to calculate averages per region.

2. Step 2: Filter out regions with no sales

   Use HAVING AVG(amount) > 0 to exclude groups where average is NULL or 0 (no sales).

3. Step 3: Check other options

   SELECT region, AVG(amount) FROM sales WHERE amount IS NOT NULL GROUP BY region; (SELECT region, AVG(amount) FROM sales WHERE amount IS NOT NULL GROUP BY region;) filters NULL rows before grouping but includes regions where non-NULL amounts average to 0. Options C and D have syntax errors or misuse WHERE with GROUP BY.

4. Final Answer:

   SELECT region, AVG(amount) FROM sales GROUP BY region HAVING AVG(amount) > 0; -> Option A

5. Quick Check:

   Use HAVING to filter groups by AVG() [OK]

Hint: Use HAVING to filter groups after GROUP BY [OK]

Common Mistakes:

• Using WHERE instead of HAVING to filter groups
• Not excluding NULL averages
• Misplacing WHERE clause after GROUP BY